1. Field of the Invention
The present invention relates to a hydro-mechanical transmission having a hydrostatic unit and a mechanical portion including a planetary gear system and in particular to such a transmission having a ball bearing mounting the carrier of the planetary system to facilitate movement of the hydrostatic unit relative to the transmission housing and the mechanical portion.
2. Description of Related Art
In hydro-mechanical transmission having a mechanical portion and a hydrostatic unit, it is known to mount the hydrostatic unit within the transmission housing by an isolation mounting system. The isolation mounting system uses a resilient member, such as a rubber member, to isolate the hydrostatic unit from the housing. This reduces noise and vibration transmission from the hydrostatic unit to the transmission housing. The resilient member allows limited movement of the hydrostatic unit relative to the transmission housing. An example of such a mount is shown in U.S. Pat. No. 5,345,839 where rubber members 17b and 21a, FIGS. 3 and 4, are used to dampen noise and vibration from the hydrostatic unit. With the use of a resilient isolating mount for the hydrostatic unit, it is necessary to accommodate the movement of the hydrostatic unit in the mechanical portion of the transmission to avoid premature wear of the gear faces.
The present invention overcomes the problem of premature wear of the gear faces by providing the mechanical portion of the transmission with a planetary carrier that is mounted on a ball bearing instead of taper roller bearings. A ball bearing is typically manufactured with internal clearances to allow a small amount of misalignment. The ball bearing thus allows the carrier limited movement transverse to the axis of rotation of the carrier. To further reduce wear of the gear faces, one or more of the meshing gears at the point of relative movement have crowned gear faces rather than straight gear faces to avoid a single line of contact of the meshing teeth at the tooth edge.